implement extendable first run experience starting with welcome page

src/main/java/io/lbry/browser/reactmodules/FirstRunModule.java

@@ -0,0 +1,44 @@
+package io.lbry.browser.reactmodules;
+
+import android.content.Context;
+import android.content.pm.PackageInfo;
+import android.content.pm.PackageManager;
+import android.content.SharedPreferences;
+
+import com.facebook.react.bridge.Promise;
+import com.facebook.react.bridge.ReactApplicationContext;
+import com.facebook.react.bridge.ReactContextBaseJavaModule;
+import com.facebook.react.bridge.ReactMethod;
+
+import io.lbry.browser.MainActivity;
+
+public class FirstRunModule extends ReactContextBaseJavaModule {
+    private Context context;
+
+    private SharedPreferences sp;
+
+    public FirstRunModule(ReactApplicationContext reactContext) {
+        super(reactContext);
+        this.context = reactContext;
+        this.sp = reactContext.getSharedPreferences(MainActivity.SHARED_PREFERENCES_NAME, Context.MODE_PRIVATE);
+    }
+
+    @Override
+    public String getName() {
+        return "FirstRun";
+    }
+
+    @ReactMethod
+    public void isFirstRun(final Promise promise) {
+        // If firstRun flag does not exist, default to true
+        boolean firstRun = sp.getBoolean("firstRun", true);
+        promise.resolve(firstRun);
+    }
+
+    @ReactMethod
+    public void firstRunCompleted() {
+        SharedPreferences.Editor editor = sp.edit();
+        editor.putBoolean("firstRun", false);
+        editor.commit();
+    }
+}